The field of invention relates to optical communication devices in general; and, more specifically, to optical polarization modulators and compensators.
There are various methods to transmit information in fiber-optic communication systems. Some optical communication systems use state of polarization (SOP) modulation to transfer information. In a typical optical SOP system, a polarization modulator is used to control the SOP of an optical signal (i.e., a laser beam) by changing the phase and amplitudes of the optical signal""s TE (transverse electrical) and TM (transverse magnetic) components (these components also referred to herein as the TE and TM components). The SOP can be used to achieve multi-level transmission (i.e., where each SOP can represent the value of multiple bits). SOP-based optical communication systems can be substantially insensitive to some nonlinear fiber effects, such as self-phase modulation and polarization dependent gain in some EDFAs (Erbium doped fiber amplifiers).
Some polarization modulators use the thermo-optic effect to modulate the SOP. However, the speed of these thermo-optic based polarization modulators and compensators is relatively slow with typical symbol rates in the kHz range.
Other polarization modulators use Lithium Niobate (LiNbO3) devices, which provide greater symbol rate, but are relatively high in cost, form factor, and difficulty in implementing in an integrated circuit device.